准噶尔盆地乌尔禾油田高自然伽马砂砾岩特征及其沉积微相研究——以乌36井区百口泉组为例

High GR Glutinite Feature and Micro-Sedimentary Facies in Wuerhe Oil-field,Junggar Basin——Taking the Baikouquan Group in Wu 36 Area as an example

基于岩芯编录、测录井资料和薄片分析数据,对准噶尔盆地乌36井区三叠系百口泉组开展了沉积学研究。研究表明,乌36井区百口泉组发育冲积扇沉积体系,扇体内部砂砾岩具有自然伽马异常高的特点,而泥岩具有自然伽马异常低的特点,其原因主要是由于原岩碎屑中富含凝灰岩等高放射性物质,同时沉积物的粒度变化、搬运距离和相带展布控制了砂砾岩自然伽马异常的空间变化,并依据伽马异常的空间变化特点建立了相应的泥质含量计算公式,提出了高自然伽马砂砾岩沉积微相划分的一种新方法。区内主要发育冲积扇扇中辫流线微相、扇中辫流砂岛微相、扇中漫洪带微相和扇缘漫流带微相。精细刻画了各期扇体沉积微相的展布与垂向演化特征,百口泉组三段发育四期扇体,垂向上表现为一个快速水退背景和缓慢水进背景下的沉积演化序列;百口泉组二段发育三期扇体,垂向上表现为退积型演化序列;百口泉组一段则表现为冲积扇扇缘沉积。通过与实际生产对比,本次研究较好地解释了区内生产井的生产状况,验证了利用高自然伽马砂砾岩自然伽马特征研究沉积微相的可行性与实用性。

Based on rock core documentation,well logging analysis and the rock fragment data,we carried out the sedimentology research on the Triassic Baikouquan Group in Wu 36 area of Junggar Basin. This study revealed that the Baikouquan Group developped in alluvial fan system. The glutenite is characterized by unusually high natural gamma and the mudstone is characterized by low inside the alluvial fan. This feature is mainly controlled by the high radioactive substance in the original rock,for example the tuff. The spatial variation in high natural gamma anomaly was influenced by sediment grain size,transport distance and facies distribution. According to the spatial variation characteristics of Gamma anomaly,we established a clay content formula and put forward a new method on the division of sedimentary facies. Our study area mainly develops mid-fan braided stream line microfacies,mid-fan braided stream sand island microfacies,mid-fan sheetflood microfacies and cross flow microfacies in marginal subfacies. We also carefully portrayed the distribution and vertical evolution of these sedimentary microfacies of different stages. The results show that the 3rdmember in Baikouquan Group developed four fan bodies. There is a sedimentary evolutionary sequence in the vertical profile controlled by fast dereliction and slow retrograding. The 2ndmember in Baikouquan Group developed three fan bodies and presented a retrograding evolutionary sequence in the vertical. The 1stmember in Baikouquan Group performed the alluvial fan marginal sedimentary. Compared with the actual production,this study better explained the production status of the regional producing well and verified the feasibility and practicality of using natural gamma characteristics of high natural gamma glutinite to make research on sedimentary microfacies.